Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
FIG. 1 shows a conventional semiconductor die 10 with contact pads 12 formed on active surface 14. A plurality of bumps 16 is formed over contact pads 12. Substrate 10 is mounted to substrate or test bed 20 with bumps 16 electrically connected to conductive layer 22.
A common test for semiconductor die 10 is electro-migration testing, which involves routing a large DC test current ITEST through the interconnect under test. The electron momentum associated with the large DC current causes metal atoms from the bump and conductive layers under test to move with the current flow. When a sufficient number of metal atoms have been displaced from the bump under test or conductive layers under test due to electro-migration, the low-impedance interconnect integrity breaks down to an open circuit condition. Electro-migration is a principal cause of interconnect defects and failures in semiconductor devices. Measurement of electro-migration characteristics is important in establishing design guidelines to ensure adequate long-term reliability.
To test electro-migration, the DC test current ITEST is divided between conductive layer 22b-22d, bumps 16b-16d, and conductive layer 12b-12d. The full DC test current flows through conductive layer 12a, bump 16a, and conductive layer 22a as the interconnect under test. The electro-migration testing is a long process, typically over a number of months, to determine how long bump 16a and conductive layers 12a and 22a can withstand a given DC test current before failure, i.e., before the bump or conductive layer breaks down to an open circuit condition.
The configuration of substrate 20 accommodates a single interconnect under test, i.e., bump 16a and conductive layers 12a and 22a. Given that a large number (hundreds) of interconnects must be tested concurrently, substrate 20 requires many power supplies to generate the individual DC test currents. The large number of power supplies and complex wiring needed to perform the electro-migration testing involves significant cost.
FIG. 2 shows another known electro-migration testing arrangement with semiconductor die 30 having contact pads 32 formed on active surface 34. A plurality of bumps 36 is formed over contact pads 32. Substrate 30 is mounted to substrate or test bed 40 with bumps 36 electrically connected to conductive layer 42. The DC test current ITEST is routed through bumps 36 and contact pads 32, and conductive layer 42 in a daisy-chain arrangement to test all bumps 36 simultaneously. However, the electro-migration testing ends with the first bump to fail as the DC test current path is broken. The DC test current no longer flows through the remaining bumps 36. The daisy-chain arrangement measures only the weakest bump in the chain and therefore samples only a portion of the statistical distribution.